Currently, commercial solar photovoltaic (PV) modules are divided into two categories, one is the bulk crystalline silicon solar cells and polycrystalline silicon solar cells, etc., and the other is thin-film solar cells, such as silicon series, copper indium gallium selenide series, and cadmium telluride series, etc., solar cells. Further, based on the type of the substrate used, thin-film solar cells can be divided into hard substrate solar cells and flexible substrate solar cells.
Thin-film solar cells currently on the market are mainly based on glass substrates, which belong to the hard substrate solar cell category. Such solar cells currently have the largest market share. The flexible substrate solar cells have less share of the solar cell market. The flexible substrates used in the solar cells include conductive materials, such as stainless steel strip and copper strip, etc., and insulation materials, such as polyimide.
U.S. Pat. No. 6,858,461 and U.S. Pat. No. 4,795,500 respectively disclose solar photovoltaic modules with different light transmittances made on a transparent TCO glass substrate using a laser to etch the light absorbing layer and the back metal-electrode-layer film. Based on the above U.S. Patents, Japanese Patent JP2003003956 and Chinese patent CN200480001786.3 realize ordered control on the size of openings (diameter 30˜500 μm), opening spacing (1.01 to 2 times the diameter), and lattice by controlling the on-off frequency of the laser and the relative scanning speed of the laser between the laser and the substrate. These patents have the common feature of using laser to etch the light-absorbing layer and the back metal-electrode-layer film to achieve light transmittance. However, its drawback is that the high-energy plasma generated by laser etching can melt the back metal and directly cause short circuit between the front electrode and the back electrode on the surfaces of the etching area, and crystallization of particles of amorphous silicon. This can increase the leakage current, decrease the fill factor, and thus destroy the battery performance.
Chinese Patent 200710073014.6 discloses a flexible solar cell based on modified polyimide substrate. The polyimide film is light-weighted, low cost, and completely transparent after modification, with a light transmittance rate of 93%, and the photoelectric conversion efficiency is improved. However, the convergence techniques, such as affinity between the solar cell substrate and the packaging material, still needs to be improved to increase the light transmittance, to reduce product cost, and to meet the various requirements of the market, especially in the green photovoltaic building field.